The efficacy and toxicity of three immunosuppressive drug regimens will be evaluated in patients with membranous lupus nephropathy over a 12 month study period. Detailed tests of renal function, glomerular permselectivity and kidney biopsy morphology will be conducted at the beginning and end of treatment. Patients with systemic lupus erythematosus, nephrotic range proteinuria and biopsy documented membranous nephropathy will be treated with alternate day prednisone and will be randomized to receive: a) no additional therapy (control group), b) intravenous pulse cyclophosphamide up to 1.0 gram per square meter body surface area every other month for 6 total doses, or c) oral cyclosporin A up to 200 mg per square meter body surface area daily for a total of 11 months. Lupus disease activity, renal function tests and drug toxicities will be monitored closely. Analysis will include comparison of the number of favorable outcomes of glomerular function and pathology as well as drug-related toxicities appearing in each treatment group at the end of 12 months of study.